Purification plant for aeration of sewage

ABSTRACT

A process and a purification plant for the aeration of sewage in an aeration tank with displaceable aeration means arranged close to the bottom of the tank.

PURIFICATION PLANT FOR AERATION OF SEWAGE This invention relates to a process'and purification plant for the aeration of sewage in an aeration tank, using displ'aceabl aeration means arranged close to the bottom of the installation.

' It is known that the use made of the oxygenin the'aeration" A of sewage or mixtures of sewage and activated sludge is more thorough if the air bubbles are introduced into the flowing water or sewage, see for example, the article fA new development in pressure air aeration (translation) by A. Pasveer and S. Swe'eris, Research Institute for public health engineering T.n.0 Working Report, 27th.,' Nov. 1962," and German Specification No. 1,202,227IAccrding to that article, the air bubbles'ascend at diminished velocity and over a larger travel path to' the surface'and the timed contact of the air bubbles with the water is increased relatively to what happens when air bubbles are introduced froma stationary aerating device'into water which is not moving.'The air bubbles introduced then one radial partition which is formed with recesses for the *passa'ge of the air feedpipes and has air distributors extending substantially over the entire tank width. In this case, the radial partitions serve for braking the waterfiow.

The aeration bridge is placed intocrotational movement either by means of an e lectricjmotor or by means of the air emerging from the attached air, distributors. Due to the subdivision of the annular aeration tankby means of one or more partitions, a rotary circular movement of the sewage due to the rotary movement'of the air distributors is prevented, even at velocities ,of about 80 cmJ s. The recesses formed in the parti'tions are only sufficiently large as is necessary for unhinascending along the shortest path, vertically to'the water surface and doing-so at the ascending velocity of the'air bubbles in nonflowing water plus the ascendingvelocity of the water, is constrainedly adjusted by means of the air bubbles. v I

The invention proceeds from the fact that more-thorough use of oxygen is achieved if a horizontal relative velocity is attained between the air bubbles introduced and therwater. The

thorough use of the oxygen is then the same, whether the aeration device is displaced horizontallyin the water at-a predetermined velocity or whether thewater flows, at the same velocity; horizontally over a stationary aeration device.

It is an objec'tgof the present-invention 'to provide, while making use of this realization, a'process and purificationplant of th'etype mentioned at the outset, wherein with regard to the air bubbles introduced, a long travel path is-constrainedly impartedand the-desired purification effect is attained with'the minimum of expenditure. To thisend, the'invention proposes a process characterized in that the air'distribu'tors arefin the case of longitudinal tanks," reciprocat'c'd overthe' tank bottom at a velocity of more than cm./s. and, in the case of annular tanks, displaced in such manner that they rotate continuously and further characterized'in that; in the case'of annular tanks,

the waterflow produced is so braked atat least one point that a rotating circular flowis prevented entirely or for the greater part. i

distributors have imparted to them rapidlyv reciprocating movement and, at the same time, air is blown infDueto the" braking of the waterflow, the air bubbles emerging from the dered passage of the air distributors and the air feedpipes associated therewith; e 1

It is, however,' also possible to provide the recesses with flaps which open and close on passage of the air feedpipes and air distributors, sothat throughflow of the water is entirely prevented, the flaps only openingwhen the air feedpipes and the air distributors travel through the recesses. lt is a furtherobject of the invention to so arrange the feed- .pipe of the return flow-sludge out of the secondary settler, the

, feedpipe of the untreated water and the position of the partitions so that the purification processtakes place in accordance with the known contact stabilization process.

For a better understanding of the invention and to show how it may be carried'into effect, the same will now be described by way' of example, with reference to the. accom- Y showing an annular tank of the purification plant operating in In the case of the process according to the irivention,-the air I air distributors are vigorously deflected from the vertical; so

that the air bubbles arereq'u'ired to travel over a relatively long path in the sewage so that in this way ensuring the introduction of oxygen in an economic manner as compared with the prior art. At the same time, sewage-activated sludge mixtures and any deposits which there may be on the tank bottom,1continue to be whirled up'and held in suspension. i

partying drawings, in which:

FIG. 1 is a sectional view and taken on linel-l'bf FIG. 2,

accordance with theac'tivated sludge process, and I FIG; 2 isaplan viewot' theannular tank according to FIG.

In the individual figures: e

6 designates the tank'bottom of the elongated tank 1,

7 designates the inner wall of an annular tank 11 8 designates the outerwall of the annular tank 1 l,

9 designates the'aeration bridgefor the annular tank l1,

l0 designatesair feedpipes leading to the air distributors 5, ll designates anaeration tank designed as an annular tank, 12 designates a partition in the annular tank 11, l3tlesignates recesses (or apertures) in the partition 12,

5 f1?! designates flaps at the recesses 13,

settlerstank '15, 34'designates-the down and calming shaft in .T he clarification plant according to the invention'for the performance of the process, has an .elongatedtank and an aeration device di'splaceably' arranged on the .longitudinal walls of the tank, and is characterized in that the air'distributors extend substantially over the entire tank width. In order'to brake or retain the content of the tank, use is made of the end face walls of the elongated tank,'except for minor conditions resultingfrom damming-up effects. a

A reciprocating device is, in practice, with regard to operating reliability, more liable to breakdown than is a device which thesecondary settler tank 15,-

35 designates the overfall' threshold in the secondary settler tank 15,

36 designates the discharge pipe into the draining ditch or canal,

37 designates the sludge removal shaft,

, 38 designates the sludge scraper; Y I

An activated sludge installation of annular design" operating in accordance with theprocess of the invention is shown by I way ofexamplein FIGS. 1 and 2; This installation comprises a is uniformly displaced, without interruption, in one direction only. Thus, for the performance of the process according to" the invention, there is furthermore proposed a purification plan having an annular tank, and an aeration bridge is mounted-for rotation about the tank center point, and having air feedpipes secured theretoand air distributors connected to the latter. Further there is arranged in the annular tank at least central tank 15, which may be used for secondary settling, for mechanical prepurification or sludge stabilization or oxidation, and an aeration tankdesigned as an annular tank 11 and surrounding the said central tank. The inner wall between the central tank 15 and the. annular tank 11 is designated by reference character 7. A bearing 31' is provided in the center point of the entire installation on which an aeration device 3 is pivotally' mounted and consisting of an aeration bridge 9.

9. The aeration bridge 9, with the air distributors 5, is driven either by means of a travel mechanism 32, driven by an elec;

stationary conduit 18, in the sense of the direction of rotation of the aeration bridge 3, behind the partition 12, into the antric motor and supported on the outer wall 8 of the annular tank 11 or by means of the guide faces (not shown) arranged in uniformly inclined positions over the air distributors accordingto the U.S. Pat. No. 3,336,016, the said guide faces being secured to the aerating device 3.

Built into the annular tank 11 is a partition 12 for preventing the tank content from passing, on rotation of the air feedpipe with the air distributors 5, into a rotating circular flow.

The partition 12 has apertures 13 which are only of sufficient size to insure that the air feedpipe l0 and the air distributors 5 are able to rotate without hindrance in the annular tank 11. As this takes place, it is true that a slight rotational flow will take place through the apertures 13 in the sense of the rotational movement of the aeration device 3, but this does not influence the introduction of nitrogen to any particular extent. However, it is also possible (as can be seen from FIG. 5) to fit flaps 14 over the apertures 13 and which are opened on passage of the air feedpipe l0 and the air distributors 5 and thereafter close again.

in the case of an activated sludge plant having an annular aeration tank 11 according to FIGS. 1 and 2, the sewage to be purified enters through the feed conduit 19, flows into the annular tank 11, is there aerated and freed by the activated sludge from dirt, in particular organic dirt, which is disadvantageous to the operation of the draining canal. It then flows, mixed with activated sludge, through the pipeline 33, into the central downwardly directed and calming shaft 34, and then passes into the secondary settler tank 15 where it rises only sufficiently slowly to ensure that the sludge particles dropto the bottom and the water is fed, with the'sludge removed therefrom over the overfall threshold 35 and over the discharge conduit 36 to the drain'canal. The sludge deposited within the secondary settler tank 15 is, as shown in FIG. 1, conveyed by means of a sludge scraper 38 secured to the aeration bridge 9 and a pump (for example a mammoth pump 16) into the annular tank 11. The sludge scraper 38 may however, also be driven, by means of reduction gearing, by the aeration bridge 9 at a speed lower in itself.

Arranged at the surrounding wall 8 is a sludge removal shaft 37 by means of which activated sludge developing in the annular tank 11 may be withdrawn.

This installation according to FIGS. 1 and 2 (illustrated by way of example) may, however, also be operated in accordance with the activated sludge purification process of the contact stabilization process, that is, the activated sludge is aerated for a relatively long period of time, then has unpurified sewage fed thereto. and, even'after a short period of aeration, the mixture of sewage and activated sludge flows into the secondary settler tank. From there, it flows, after sludge has been removed therefrom, into the drain ditch or canal, whereas the deposited sludge from the secondary settler tank is serated for a longer period of time in another tank and is also keptin suspension and only after this has been done, once again aerated together with the untreated sewage to be purified.

This purification process takes place when the infeed 19, the partition 12, the feed means 33 to the secondary settler tank 15 and the means for returning the activated sludge into the annular tank are provided in the manner shown in FIG. 5. With this arrangement, the deposited sludge is conveyed out of the center of the secondary settler tank 15,-by means of a nular tank 11 as far as the infeed 19, without unpurified sewage being fed thereto. This sludge is, thereby, aerated within half the aeration space of the annular tank 11 and the infeed 19., this aerated activated sludge is mixed with the sewage to be gurified and both are aerated and both flow to a pomt before t e partition 12. The sludge particles very rapidly take upthe released and colloidal substances of the unpurified sewage, so that the sewage isable to flow, by means of the secondary settler tank 15, fully biologically purified, through the discharge conduit 36 to the discharge outlet. By means of the apertures 13, the sludge concentration may be kept at a higher level within the aeration chamber, in particular in the reaeration chamber (between the partition 12 and the infeed 19), so that a, greater degree of stability and improved purification is achieved than would be achieved if the return flow sludge were to be conveyed out of the secondary settler tank and by means of the pipe 17 secured to the aeration device 3, in such manner as to flow continuously into the annular tank 11.

In this way, it becomes possible to purify sewage satisfactorily and economically, using relatively simple means.

We claim:

1. Sewage plant for the aeration of sewage comprising an .annular aeration tank, an aeration bridge mounted rotatably around the center of the tank, driving means for the rotation of the bridge, air feedpipes attached to the bridge at the ends of which air distributors are mounted and located near the bottom of the tank, and at least one radial separating wall in the tank with recesses therein for the passage of the air feedpipes and the distributors upon the rotation of the bridge.

2. Purification plant according to claim 1, in which at least one radial partition is arranged in the annular tank and formed with apertures for the passage of the air feedpipes and air distributors.

3. Purification plant according to claim 1, in which at least one radial partition is arranged in the annular tank and formed with apertures for the passage of the air feedpipes and air distributors and in which apertures are provided with flaps in the partition which open and close on passage of the air feedpipes and air distributors.

4. Purification plant according to claim 1, in which a tank is provided within the annular tank serving for secondary settling or purification or for mechanical prepurification or for sludge oxidation, and in which a sludge scraper is provided extending from the aeration bridge or an air distributor extending from the aeration bridge.

5. Purification plant according to claim 4, in which an airlift pump if provided for conveying the return flow sludge out of the secondary settler tank into the annular tank, the airlift pump being secured to the aeration bridge to rotate therewith.

6. Purification plant according to claim 4, in which a pipe for conveying the return flow sludge out of the secondary settler tank into the annular tank, is arranged to be stationary and rearwardly of the partition relatively to the direction of rotation of the aeration bridge.

7. Purification plant according to claim 1, in which infeed is provided for the nonpurified sewage in a zone provided relative to the direction of rotation of the aeration bridge so that the purification takes place in accordance with the contact stabilization process.

8. Sewage plant according to claim 1, in which the air distributors rotate continuously with a speed of at least 20 cm./per second. 

2. Purification plant according to claim 1, in which at least one radial partition is arranged in the annular tank and formed with apertures for the passage of the air feedpipes and air distributors.
 3. Purification plant according to claim 1, in which at least one radial partition is arranged in the annular tank and formed with apertures for the passage of the air feedpipes and air distributors and in which apertures are provided with flaps in the partition which open and close on passage of the air feedpipes and air distributors.
 4. Purification plant according to claim 1, in which a tank is provided within the annular tank serving for secondary settling or purification or for mechanical prepurification or for sludge oxidation, and in which a sludge scraper is provided extending from the aeration bridge or an air distributor extending from the aeration bridge.
 5. Purification plant according to claim 4, in which an airlift pump if provided for conveying the return flow sludge out of the secondary settler tank into the annular tank, the airlift pump being secured to the aeration bridge to rotate therewith.
 6. Purification plant according to claim 4, in which a pipe for conveyIng the return flow sludge out of the secondary settler tank into the annular tank, is arranged to be stationary and rearwardly of the partition relatively to the direction of rotation of the aeration bridge.
 7. Purification plant according to claim 1, in which infeed is provided for the nonpurified sewage in a zone provided relative to the direction of rotation of the aeration bridge so that the purification takes place in accordance with the contact stabilization process.
 8. Sewage plant according to claim 1, in which the air distributors rotate continuously with a speed of at least 20 cm./per second. 